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1.
Yong-Chan Chung Sang Hyeon Kim Jin Cheol Bae Byoung Chul Chun 《Fibers and Polymers》2018,19(6):1157-1165
The bulky and rigid triphenylmethyl group was grafted onto polyurethane (PU) to reduce the molecular attractions between hard segments and to improve the mobility of the PU chain under freezing conditions. The triphenylmethyl-grafted PU exhibited improvement in the cross-link density, solution viscosity, maximum tensile stress, shape recovery at 10 °C, and low temperature flexibility compared with the plain PU. The soft segment melting was not affected by the grafted triphenylmethyl group, whereas the soft segment crystallization disappeared with the increase of the triphenylmethyl group content. The glass transition temperature (Tg) increased with the increase of the triphenylmethyl group content. The rapid increase of the tensile strength and shape recovery at 10 °C resulted from the cross-linking effect, whereas the strain at break and shape retention at -25 °C slightly decreased with the increase of the triphenylmethyl group content. The triphenylmethylgrafted PU displayed an excellent low temperature flexibility even at -50 °C due to the improved mobility of the PU chain compared to ordinary PU. 相似文献
2.
Alizarin-series dyes (alizarin, alizarin red S, alizarin yellow GG, or mordant orange) are grafted onto shape memory polyurethane (PU) through an allophanate bonding, and the photoluminescence and the low-temperature flexibility of the resulting PUs are tested. The PU is mainly composed of 4,4′-methylenebis(phenylisocyanate) (MDI), poly (tetramethyleneglycol) (PTMG), and 1,4-butanediol (BD), and the dye is connected, through another MDI, to the carbamate moiety of the PU chain. The PUs with different dye contents are characterized, and their shape recovery and photoluminescence properties are compared. With respect to the tensile mechanical properties, the maximum stress increases up to 50 MPa, and the strain remains above 1000 % even after the dye is grafted onto the PU. The shape recovery is as high as 99 %, and the shape retention improves as the dye content increases. Finally, the photoluminescence of the PUs is demonstrated by the luminescent light emission test, and the dye-grafted PU shows excellent low-temperature flexibility compared with that of linear PU. 相似文献
3.
The grafted 3,5-dimethylphenyl group remarkably improved the low temperature flexibility of a polyurethane (PU) copolymer.
The rigid and blunt shape of 3,5-dimethylphenyl was designed to interrupt molecular interactions and to disturb the close
contact between PU chains and, thus, to improve the flexibility at extremely low temperature, while maintaining high and reproducible
tensile and shape memory properties at ambient temperature. The effect of the 3,5-dimethylphenyl group on the flexibility
of PU was tested at −30 °C together with a linear PU, and the reason for the exceptional flexibility at low temperature is
discussed. 相似文献
4.
Effect of the pendant n-butyl group on shape recovery and tensile properties of polyurethane (PU) block copolymer was investigated. The grafted n-butyl group was intended to keep PU chains away and to deter molecular interaction between PU chains by its flexible chains,
and thus improve shape recovery at subzero temperature while maintaining high and reproducible tensile properties and shape
recovery at ambient temperature. The attachment of n-butyl group did not make any change in the molecular interaction and phase separation of hard and soft segments in PU structure
as judged from IR and DSC analysis. Cross-link density and intrinsic viscosity increased with the increase of n-butyl content due to the partial cross-linking by the linking reagent. Shape recovery and shape retention were not diminished
after cyclic shape memory tests. Finally, the effect of n-butyl group on low temperature shape recovery was compared with linear ones and the potential application of this finding
was discussed. 相似文献
5.
The prepolymer and the final polyurethane (PU) block copolymer were synthesized by reacting 4,4-methylene bis(phenylisocyanate)
with poly(tetramethylene glycol) and the prepolymer with 1,4-butanediol as a chain extender, respectively, to investigate
the relation between phase separation and it’s resulting properties. According to FT-IR data, the phase separation of hard
and soft segments in the prepolymer and the PU block copolymer grew bigger by increasing the hard segment content, and the
PU showed more dominant phase separation than the prepolymer. The heat of fusion due to soft segments decreased in both the
prepolymer and the PU by increasing the hard segment content, whereas the heat of fusion due to hard segments increased in
the PU did not appear in the prepolymers. The breaking stress and modulus of the prepolymer increased by increasing the hard
segment content, and the elongation at break decreased gradually, and the PU showed the highest breaking stress and modulus
at 58 % hard segment content. However, the best shape recovery of the PU was obtained at 47 % hard segment content due to
the existence of proper interaction among the hard segments for shape memory effect. Consequently, the mechanical properties
and shape memory effect of the PU were influenced by the degree of phase separation, depending on the incorporation of chain
extender as well as the hard segment content. 相似文献
6.
Yong-Chan Chung Duy Khiem Nguyen Jae Won Choi Byoung Chul Chun 《Fibers and Polymers》2010,11(7):952-959
Effect of glucose cross-linking on the shape memory and mechanical properties of polyurethane (PU) block copolymer was investigated.
Glucose was selected due to its large number of free hydroxyl groups, easy availability, miscibility with other reactants,
and cyclic structure. The glycerol cross-linking did not affect the molecular interaction and phase separation of hard and
soft segments in polyurethane structure as judged from IR and DSC analysis. Viscosity of glucose cross-linked PU increased
after cross-linking due to the cross-linked structure. Maximum stress drastically improved with the adoption of glucose as
a cross-linker together with a slight increase in strain at break. Shape recovery also increased with the adoption of glucose
as a cross-linker, and shape recovery was not diminished after four cyclic shape recovery tests. In contrast, shape retention
significantly decreased if glucose was included for two different hard segment contents. Finally, glucose cross-linking was
compared with other cross-linkers used in shape memory polymer and the advantage of glucose cross-linking was discussed. 相似文献
7.
The polyurethane (PU) copolymer was grafted with either 3-dimethylaminopropanol as a basic pendant group or 4-hydroxylphenylacetic acid as an acidic pendant group. The two types of PU were mixed in solution to form ion-pairing between acidic and basic pendant groups. The structural change after grafting and ion-pairing was followed by acid-base titration, infrared spectra, differential scanning calorimetry, and absolute viscosity. The tensile stress can be raised as much as 70 % by the control of the ion-pairing ratio of acidic and basic PUs. Shape recovery was over 80 % and reproducible for four test cycles. The minor control of tensile properties of PU was possible through the ion-pairing method. 相似文献
8.
The polyurethane (PU) copolymer was laterally crosslinked with an extra MDI, in which a more rigid polycarbonatediol replaced the conventional poly(tetramethyleneglycol) as a soft segment. What is the impact of the possible molecular interaction between polycarbonate soft segments and lateral crosslinking. The structural change after crosslinking and the impact of new soft segment were followed by infrared spectra, crosslink density, UV-VIS spectra, and relative viscosity. The tensile stress could improve as much as 554 % by selecting the polycarbonate soft segment and the lateral crosslinking. Shape recovery was over 90 % for the entire series and reproducible for four test cycles. The adoption of polycarbonate soft segment and lateral crosslinking significantly could improve the tensile strength and shape recovery compared to PU with polyetherdiol or polyesterdiol soft segment. 相似文献
9.
Composites consisting of polyurethane (PU)/carbon nanotubes (CNTs) have been successfully prepared by solution mixing method. CNTs were modified through mechano-chemical reaction to increase the compatibility with PU via hydrogen bondings. SEM microphotographs proved that modified CNTs (M-CNTs) became shorter and FTIR spectra showed that hydroxyl groups had been introduced to the surface of M-CNTs. SEM images of PU/M-CNTs composites also proved that M-CNTs were effectively dispersed in PU matrix. Mechanical property tests showed that addition of M-CNTs could significantly improve the tensile properties of PU/M-CNTs composite (breaking strength enhancement ratio for composite with 5.0 wt% M-CNTs was 103.81 %). The thermal stability of composites with M-CNTs was also improved. The initial degradation temperature enhancement was 19.9 oC for the composite with 0.5 wt% M-CNTs. Electrical property tests showed that the electrical properties were improved by adding M-CNTs. The volume conductivities increased 3 and 5 orders of magnitude for the composites with 5.0 wt% and 10 wt% M-CNTs, respectively. The addition of M-CNTs had little effect on the elastic properties of the composites. 相似文献
10.
Myeong Jun Jo Howon Choi Ga Hee Kim Woong-Ryeol Yu Miseon Park Yeontae Kim Jong Kyoo Park Ji Ho Youk 《Fibers and Polymers》2018,19(9):1799-1805
In order to develop epoxy shape memory polymers (ESMPs) with high switching temperature and excellent toughness for deployable space structures, the crosslink density and chain flexibility of candidate ESMP samples were tunned by adding two flexible poly(oxypropylene) diamines, Jeffamine D-230 (D230) and Jeffamine D-400 (D400), as a secondary curing agent. The desired switching temperature of ESMPs for deployable space structures was set within the range of 120-135°C. By adding D230 and D400, the switching temperature of the ESMPs could be adjusted to within this range by increasing their crosslink density, and their impact strength could be significantly increased due to the stress relaxation properties of the diamines’ flexible molecular chains. The modulus and tensile strength of the ESMPs increased, but elongation at break decreased, in proportion to the diamine content. The ESMPs with a suitable switching temperature for deployable space structures had a high elongation at break greater than 22 % and good shape recovery and shape fixity ratios. The larger the value of shape recovery ratio, the faster the shape recovery speed. 相似文献
11.
Nanocomposites of polyurethane (PU) and multi-walled carbon nanotubes (MWNTs) were prepared via in-situ polymerization of
poly(ɛ-caprolactone)diol (PCL)-grafted-MWNTs, 4,4′-methylene bis(phenyl isocyanate), and 1,4-butanediol. The grafting of PCL
onto MWNTs was confirmed by Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The
nanocomposites showed more improved mechanical properties compared to conventional nanocomposites with the same MWNT loading.
The thermo-responsive shape recovery as measured in a cyclic tensile test was observed to be approximately 80 % for in-situ
nanocomposites, though it showed a reduced trend as the wt% of MWNTs increased. X-ray diffraction investigation also showed
that the addition of MWNTs into the polyurethane increased the crystallinity. Scanning electron microscopy and TEM measurements
showed better dispersion of MWNTs in the nanocomposites synthesized using in-situ method. Consequently, the presence of PCL-g-MWNTs
made an important contribution to the enhancement of the mechanical and shape memory properties of polyurethane. 相似文献
12.
Jong Shin Park Yong-Chan Chung Sang Do Lee Jae Whan Cho Byoung Chul Chun 《Fibers and Polymers》2008,9(6):661-666
The shape memory polyurethane (PU) copolymers cross-linked by celite, a porous inorganic material with enormous surface area
and hydroxyl groups on the surface, were prepared to see if the shape memory effect and the mechanical properties were improved.
The PU copolymers with different celite contents were compared and characterized by IR, DSC, DMA, and UTM. The melting temperatures
of PU soft segment were around 20 oC independent of celite content. The shape memory effect and mechanical properties were
dependent on the celite content, and the celite addition into the reaction mixture should be made in the middle of polymerization
to get the best shape memory and mechanical properties. The best mechanical properties were found at 0.2 wt% celite content
and its shape retention rate went up to 98 %. The inclusion of celite as a cross-linker increased both shape memory effect
and mechanical properties. The reasons underlining the improvements by adopting celite as a cross-linker are discussed in
this paper. 相似文献
13.
Jung-Min Lee Sung-Hoon Kim Heon-Young Jeong Na-Rang Ahn Hyun-Gyoo Roh Jae-Whan Cho Byoung-Chul Chun Senung-Taek Oh Jong-Shin Park 《Fibers and Polymers》2014,15(7):1349-1356
Polyurethanes are polymers with urethane linkages in their backbone. It is prepared by polyaddition polymerization between isocyanates and polyols, which produce different chemical, physical, and mechanical properties depending on their types and characteristics. Previous reports of polyurethane foams prepared by using PEG polyol indicated prominent features in the elasticity and recovery of the foams. However, it is necessary to improve the mechanical strength of these materials. In this study, polyurethane foams were prepared using a PLA/PEG polyol mixture and 1,6-hexamethylene diisocyanate. PLA polyol was synthesized by the direct condensation polymerization of lactic acid. The polyurethane foams were characterized using FE-SEM analysis, FT-IR spectroscopy, water absorbency measurement, and mechanical property measurement. In FE-SEM analysis, it was shown that the PLA content of polyol mixture significantly affected the porous structure. FT-IR spectra confirmed that urethane linkages formed between the PLA/PEG polyols and the isocyanates. The water absorbency decreased due to the hydrophobicity of PLA. With respect to the mechanical properties, the breaking stress and the Young’s modulus increased with increasing PLA content. When the PLA content of polyols was 60 and 70 percent, the breaking strain was significantly higher than those of other polyurethane foams. 相似文献
14.
I. D. G. Ary Subagia Zhe Jiang Leonard D. Tijing Yonjig Kim Cheol Sang Kim Jae Kyoo Lim Jae Kyoo Lim 《Fibers and Polymers》2014,15(6):1295-1302
In this study, we report the fabrication and evaluation of a hybrid multi-scale basalt fiber/epoxy composite laminate reinforced with layers of electrospun carbon nanotube/polyurethane (CNT/PU) nanofibers. Electrospun polyurethane mats containing 1, 3 and 5 wt% carbon nanotubes (CNTs) were interleaved between layers of basalt fibers laminated with epoxy through vacuum-assisted resin transfer molding (VARTM) process. The strength and stiffness of composites for each configuration were tested by tensile and flexural tests, and SEM analysis was conducted to observe the morphology of the composites. The results showed increase in tensile strength (4–13 %) and tensile modulus (6–20 %), and also increase in flexural strength (6.5–17.3 %) and stiffness of the hybrid composites with the increase of CNT content in PU nanofibers. The use of surfactant to disperse CNTs in the electrospun PU reinforcement resulted to the highest increase in both tensile and flexural properties, which is attributed to the homogeneous dispersion of CNTs in the PU nanofibers and the high surface area of the nanofibers themselves. Here, the use of multi-scale reinforcement fillers with good and homogeneous dispersion for epoxy-based laminates showed increased mechanical performance of the hybrid composite laminates. 相似文献
15.
Yong-Chan Chung Jae Won Choi Young Jae Jung Samsook Han Byoung Chul Chun 《Fibers and Polymers》2013,14(12):2069-2076
Polyurethane (PU) copolymer is laterally linked with three kinds of metal ion indicator (calcein, calmagite, or eriochrome black T), with which free metal ion in aqueous solution is intended to be detected by PU color change. Metal ion detection by the indicator-PU fails due to the poor permeation of hydrophilic metal ion into hydrophobic PU layer. Instead, three surfactants with different ionic head groups, aerosol OT (AOT), cetyltrimethylammonium bromide (CTAB), and sodium dodecylsulfate (SDS), are tested for metal ion. Cationic CTAB exhibits an instant PU color change, but anionic AOT and SDS do not respond at all. Reason for the selective detection of cationic surfactant is the complex formation between cationic surfactant and indicator. Molecular interactions between PUs are affected by the laterally linked indicators based on the results by infrared spectra and differential thermal analysis. UV-vis spectra reveal that extra peak arising from the linked indicator appears compared to plain PU. The lateral linking of indicator to PU demonstrates, as well as the selective surfactant detection, a 454 % increase in tensile strength and reproducible shape recovery as high as 99 % compared to plain PU. 相似文献
16.
A series of crosslinked waterborne polyurethane (WBPU) adhesives were prepared by prepolymer synthesis. Modified melamine,
hexamethoxymethyl melamine (HMMM) was used as the crosslinking agent. It was elucidated by FTIR and 1H-NMR spectroscopy that the crosslinking reaction occurred between the polyurethane carboxyl acid salt groups and the HMMM
methoxy groups. The hydrophobicity of the WBPU films increased after HMMM crosslinking. As the HMMM content was increased
(increasing mole ratio of HMMM/dimethylol propionic acid (DMPA)), the water uptake (%) of the film decreased, and the water
contact angle increased. The thermal stability, tensile strength, and initial modulus increased with increasing HMMM content
up to an optimum value (mole ratio of HMMM/DMPA=0.5) at which point the maximum thermal stability, tensile strength, and initial
modulus were recorded. The adhesive strength was found to be dependent on HMMM content, curing time, and temperature. The
adhesive strength of crosslinked WBPU in the case of optimum HMMM content (8.46 wt%) was only slightly affected after immersing
adhesive bonded nylon fabrics in water (for up to 2 days). 相似文献
17.
Weilin Xu Fei Zhou Chenxi Ouyang Weigang Cui Mu Yao Xungai Wang 《Fibers and Polymers》2008,9(1):71-75
Small diameter vascular grafts were fabricated from pure Polyurethane (PU) as well as PU reinforced with a tubular weft-knitted
fabric. The tensile properties of the reinforced composite vascular grafts were compared with that of the tubular fabric itself
and the pure PU vascular grafts. The elasticity and strength of the reinforced vascular grafts were improved compared with
the tubular fabric. Strength of the reinforced vascular grafts was 5–10 times of the strength of the pure PU vascular grafts.
Expanding the tubular fabric to increase the inner diameter of the reinforced vascular graft reduced the graft’s strength
and initial modulus, but the difference was reduced as the PU content was increased. For grafts of the same inner diameter,
increasing the PU content increased the thickness and strength of the graft wall, which led to a general increase in the strength
and initial modulus of the composite vascular grafts. 相似文献
18.
In this study, polyurethane films were prepared using starch as the main polyol component, and the mechanical properties of
these films were investigated. The starch content of the polyols was 30–50 wt%. To confirm the formation of a urethane linkage
between the −OH of starch and −NCO of toluene 2,4-diisocyanate, Fourier transform infrared (FT-IR) spectroscopic analysis
was performed. Differential scanning calorimetry (DSC) thermograms of the polyurethanes resulted in two endothermic peaks,
which shifted to higher temperatures with increasing starch content and −NCO/−OH molar ratio. Due to the melting behavior
of polyurethane, films could be prepared by hot pressing at an appropriate temperature. Polyurethane films were prepared with
various polyol starch content and −NCO/−OH molar ratios. Tensile testing indicated that the breaking stress and elastic modulus
increased significantly with starch content and −NCO/−OH molar ratio. In addition, bending tests indicated an increase in
breaking stress and bending modulus with starch content and −NCO/−OH molar ratio and decreased breaking strain. The strain
rate in both tensile and bending tests had a significant effect on the mechanical properties. 相似文献
19.
Effect of cross-linking agent structure on the shape memory property of polyurethane block copolymer
Effect of cross-linking agent on the shape memory and mechanical property of polyurethane (PU) block copolymer is comprehensively
investigated. The selected chemical cross-linking agents are glycerol, 1,2,6-trihydroxyhexane, and 2,4,6-trihydroxybenzaldehyde
that are differentiated from each other in having remote hydroxyl group and aromatic ring. Significant increase in maximum
stress was observed for all of the cross-linked PUs, although the cross-linker structure was different. Structural change
of PU after cross-linking as evidenced by differential scanning calorimetry and infrared spectra was not detected, suggesting
that interaction between PU chains remained intact. Shape recovery went to as high as 95 % after cross-linking for all of
the cross-linking agents, and shape retention did not improve even if cross-linker was used. The remarkable increase in shape
recovery and maximum stress definitely originated from the employment of a cross-linking agent, and the effect of different
cross-linker structure on shape memory and mechanical property is discussed. 相似文献
20.
A series of shape memory polyurethane (PU) copolymers synthesized from 1,4-phenyldiisocyanate (PDI), poly(tetramethyleneglycol)
(PTMG), 1,4-butanediol (BD) as a chain extender, and glycerol as a cross-linking agent were tested for the mechanical properties
and the shape memory effect at the temperature 20 °C above melting temperature (T
m), and were compared with other PUs synthesized from 4,4′-methylene-bis-phenyldiisocyanate (MDI), PTMG, and BD. Mechanical
properties and shape memory effect were improved substantially by adopting both PDI and glycerol. Interestingly, enthalpy
of melting and T
m were not affected by the glycerol content. Vibration and shock absorption ability was investigated by measuring both loss
tan δ and storage modulus with dynamic mechanical analyzer (DMA). 相似文献